- A group of organisms from one species
- abundance
- sex ratios
- age structure
- Defining the population boundary…
- a lake
- ecosystem
- country or state
- Aphid population: leaf, plant, grassland, ecosystem?
- depends on the study and the questions
WHAT: Defining a population can be tricky
WHY: Understanding population structure (Demography)
- # of individuals is how we measure populations
- Age of a population, peak reproductive ages
- Sex ratios determining mating potential
- Measuring, predicting and evaluating population sizes guides ecologist
- is it growing, declining, holding steady?
Case Study: Deer population size
Case Study: Deer population density
Case Study: Zombie Deer
WHO: Definition of an individual can be tricky
- Unitary organism: forming a single entity
- deer, bird, spider, etc.
- Modular organisms are harder
- bacteria, algae, corals
- plants: ferns grow by rhizomes
- Some modular organisms may themselves be populations
HOW: Estimates from representative sample
- Lessons from Lab:
- Census techniques
- Mark & Recapture
- Spatial component
- Temporal Component
Life History: More than just birth and death
Reproductive effort and life cycles: Long lived organisms
Semelparous: One-off reproduction
Populations and life cycles: Annuals & Ephemerals
Life History: Sexual conflict
- Annuals vs Perennials
- not just plants
- When and how to spend your resources
- reproduction comes at a cost of growth
- flowers + seeds = ↓ leaves and roots
- are enough resources available to support pregnancy?
- death vs growing the population…
The mystery of large ‘Mast’ years in botany
Populations and life cycles: Dormancy
- Annual organism may spend part of the year dormant
- Seeds,Spores, Cysts, etc.
- Thousands of seeds per square meter of soil
- Dormancy can last for long periods of time
- protection from harsh environments
- How does this affect a population?
- Populations are composites of individual Life Histories
- who survived from previous year
- new individuals (births/immigration)
- survivability of offspring
Survirvorship =
Populations dynamics: Monitoring birth and death
- Measuring rates of birth and death can tell us if a population is growing or shrinking
- Cohort Life tables: follow the fate of individuals from a single cohort
- survivorship
- difficult for mobile animals
- Static life table: describe # of survivors at different ages
r/K selection theory: Growth and reproduction strategies
- r-selected species: “cheap” offspring
- K-selected species: “expensive” offspring
- These are the 2 ends of a spectrum
Populations dynamics: Movement (dispersal and migration)
Populations with unlimited resources: Exponential growth
Population growth regulation
- Density dependent
- competition
- predation
- disease
- resources
- Density independent
- weather
- disturbance
- Carrying Capacity
- environmental resistance
Population cycles
